Polymer removes dye from wastewater

The left vial shows dye solution in water (blue) and the right vial shows clear water after the dye was removed from the solution by the polymer. (Credit: Januka Budhathoki-Uprety)

A synthetic polymer can remove certain dyes from water, and can then be recovered and reused.

The findings offer a new potential method for cleaning wastewater after use by textiles, cosmetics, or other industries.

“Dyes are used everywhere, including in the textile industry, as well as in pharmaceuticals, cosmetics, paper, leather, and even in medicines,” says Januka Budhathoki-Uprety, an assistant professor of textile engineering, chemistry, and science at North Carolina State University, and lead author of the study in ACS Applied Polymer Materials.

“If these contaminants aren’t properly removed from wastewater after dyeing and finishing, they can be a significant source of environmental pollution and pose risks for human health.”

In the study, researchers made a synthetic polymer called polycarbodiimide. They then tested the material’s ability to clean wastewater first by dissolving it in a solvent, and then mixing it with water contaminated with dyes.

They tested the polymer solution against a series of 20 anionic dyes, also called acid dyes, which are used in the textile industry. For initial assessments, the researchers did a visual test with the naked eye to see if the polymer worked. The researchers later quantified how well the polymer removed the colorant using UV-Vis spectroscopy.

“We mixed the polymer solution and dye-contaminated water so the polymer in the solution can grab on to the dye. This is a two-phase solution, just like oil and water. The polymer part of the solution grabs onto the dyes,” Budhathoki-Uprety says. “Then we were able to easily separate the clean water from the contaminated solution mixture by draining it out, similar to separation of water from a mixture of oil and water.”

The polymer solution removed all but four of the 20 acid dyes they tested. In addition, they found it was easy to recover the polymer within minutes. They found characteristics of the dyes—related to their molecular structures—that contributed to whether the polymer worked or not.

“We found that the polymer solution can remove dyes from contaminated water, and we can recover the polymer and use it to remove dye from contaminated water again,” Budhathoki-Uprety says.

In future studies, researchers plan to develop a library of polymers that would have the potential to work with more types of dyes. In addition, they want to develop a more practical mechanism for using polycarbodiimide to clean wastewater.

“We are working to develop materials that can do the same work without having to use the polymer in the solution phase,” Budhathoki-Uprety says. “If you have dye spill, you don’t want to have to use a flammable solution—you want a solid material that is easier to handle.”

The Textile Engineering, Chemistry and Science Department at NC State funded the work. Individual researchers were also supported by the Office of Undergraduate Research Federal Work Study Research Assistant Program at NC State.

Source: NC State